1. Field of the Invention
Embodiments of the invention provide a method, structure, service, etc. for variable overlap of dummy shapes for improved rapid thermal anneal uniformity.
2. Description of the Related Art
Large threshold voltage (Vt) variations are found in 10S and 11S technologies. Detailed analysis shown that the cause is not Across Chip Linewidth Varaition (ACLV); instead traced to large systematic across field Vt variation. Source identified as Rapid Thermal Anneal (RTA).
Advanced semiconductor technologies require relatively sharp and shallow junctions. This forces implant diffusion and activation anneals to use very high temperatures and very short durations. Infrared RTA processes are commonly used apply this sort of spike anneal. Local variations in the reflectivity of the surface of a wafer affect the amount of radiated light absorbed by the wafer, which in turn affects the maximum temperature and the time at temperature. These variations in the local annealing conditions act to degrade the device characteristics, in some cases more severely than ACLV. The infrared (IR) reflectivity of a wafer surface is known to be strongly correlated to the local fraction of the surface not covered by diffusion (also referred to herein as “RX”) or polysilicon (also referred to herein as “PC”) features. Regions not covered by RX or PC are referred to as Shallow Trench Isolation (STI) regions. Although STI density variations occur over many distance ranges, RTA variations are known to operate over fairly large distances, typically 4 mm radius, because of the high thermal conductivity of a standard semiconductor wafer.
Dummy FILL shapes are used in the semiconductor industry to reduce the variation in local density for RX and PC features. These dummy features are primarily used to improve the manufacturing process window for the RX and PC process modules. For RX, the primary yield limiter addressed by RXFILL is Chemical-Mechanical Polish (CMP) planarization. For PC, the primary yield limiter addressed by PCFILL is linewidth variation. Although it would be useful to reduce STI density variations for improved RTA uniformity, normally it would not be possible to affect the STI density without also changing the RX or PC local density, or both.